Lightning arrester gap and grading means



April 9, 1968 Y J. c. OSTERHOUT 3,377,503

LIGHTNING ARRESTER GAP AND GRADING MEANS I Filed Oct. 1, 1965 2 Sheets-Sheet 1 50 L K mm 1 Q FIG. 6. z 0 18' "I 0 FIG. 2.

A ril 9, 1968 J. C. OSTERHOUT LIGHTNING ARRESTER GAP AND GRADING MEANS 2 Sheets-Sheet Filed Oct.

26 40 I FIG. 4.

United States Patent Ofifice 3,377,503 LIGHTNING ARRESTER GAP AND GRADING MEANS Joseph C. Osterhout, Bloomington, Ind., assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Oct. 1, 1965, Ser. No. 492,087 11 Claims. (Cl. 31536) ABSTRACT OF THE DISCLOSURE The invention comprises a plurality of voltage grading variable impedance, preionizing gap means connected across the main spark gaps in a lightning arrester unit and in parallel with a second plurality of voltage grading means of equal impedance values connected across the main gaps. Such a combination of means provides both balanced and unbalanced voltage grading for the arrester unit so that the voltage and resulting stresses on the unit are distributed equally throughout the unit until the moment of sparkover at which time the voltages across the gaps are unequal with a resulting overall, lower and more consistent sparkover voltage for more rapid discharge of surge current.

Disclosure The present invention relates to valve type lightning arresters and particularly to a novel means for pre-ionizing and voltage grading lightning arrester sparkover gaps.

Generally, valve type arresters consist of a spark gap, or a series of spark gaps of fixed lengths, connected in series With a resistance element having valve or nonlinear characteristics, that is, a resistor whose resistance decreases with increasing voltage, so that under normal voltage (operating) conditions it offers a very high resistance and at overvoltage (abnormal) conditions it offers a low resistance so as to conduct a current surge to ground with a low discharging voltage. After the discharge of the current surge, the resistance element increases its resistance to reduce the follow current at normal voltages to a small value. In other words, the series gap device normally insulates the power line to which it is connected, from ground but sparks over under a predetermined overvoltage to connect the line to ground. After the discharge to ground, the series gap acts im-. mediately to open the closed (sparkover) path to prevent the current normally flowing in the line from following in the path of the surge current.

Series gap arresters presently in production have voltage sparkover characteristics that are undesirably high and erratic. Overall arrester sparkover voltage level can be made proportionally lower than individual gap sparkover by unbalanced voltage grading means such as a resistor permanently connected across each gap in the series, such resistors being of unequal value. However, the voltage stresses that develop on the insulator plates that house and support the gap electrodes are now uneven. The uneven voltages cause increased stressing of the plates sharing the greater amount of potential. Thus, non-uniform stressing of the insulator plates is a disadvantageous result of permanently connected unbalancing resistors across the spark gaps.

Power line voltage can be evently distributed across the series gaps, with a consequent even distribution of stress, by use of an equal value shunting resistor across each gap acting as a voltage divider from line to ground. Such an arrangement fixes the potential evenly across each gap since the shunting resistors function as a potentiometer having equally spaced taps. However, with 3,377,503 Patented Apr. 9, 1968 this arrangement alone, the high and somewhat erratic.

One method of obtaining low, consistent gap sparkover is by pre-ionizing the spark gap area. In a given gap, slowly raised continuous or alternating voltage will usually produce sparkovers at relatively consistent voltages, but on rapidly applied voltages, the spark potentials vary more. A gap subjected to an impulse voltage may break down if the peak voltage reaches the DC. breakdown value provided that the gap is sufficiently irradiated so that an electron is present in the gap to initiate the spark process when the peak voltage is reached. An electron obtained by the process of ionization is thus required to consistently initiate the spark discharge. Sparkover occurs at consistent values with slowly increased voltages such as direct current or 60 cycle A.C.

sparkover voltage remains because ions usually have time to appear. With rapidly rising impulse voltages, ions may not have time to collect in the spark gap area. Thus the voltage will us until ions do appear or until the voltage produces them. Therefore, means should be provided in the spark gap area to insure a sufiicient supply of ions in order to maintain a low, consistent impulse voltage sparkover level.

The present invention provides a pre-ionizing means for series gap valve-type arresters presently in production. The operation and structure of one such type of arrester is fully shown and described in copending application Ser. No. 405,945, filed Oct. 23, 1964, by Joseph C. Osterhout, and assigned to the present assignee. Such arresters have limited space available in the arc chamber and in the area of the spark gap electrodes. Therefore in designing a pre-ionizer means for such arresters, space is an important consideration. Production cost and skills, manufacturing ease and similar considerations provide other criteria on which to base a pre-ionizing means design for existing arresters such as those that form the subject matter of the above-mentioned copending application.

Therefore, the principal object of the present invention is to provide a novel, dependable, and inexpensive pre-ionizing and voltage grading means for arrester gaps that is simple and easy to manufacture;

Another object of the invention is to provide a minia: ture pre-ionizing means and fits conveniently in the limited space available in spark gap arrester plates.

Still another object of the invention is to provide a novel pre-ioniZer-grading device that produces a consistent sparkover at the proper voltage level in a valve type arrester gap.

Yet another object of the invention is to provide a highly efiicient arrester unit by elfecting a voltage-stress balance in a lightning arrester gap stack that is unbalanced only at the moment of pre-ionizer gap sparkover.

A further object of the invention is to provide a novel frequency responsive voltage grading means for an arrester gap assembly.

Broadly, the present invention uses a single printed circuit package or module for each spark gap employing one grading resistor and one ionizing gap resistor in electrical contact with the major gap electrodes in a gap plate assembly. The basic circuit module consists of a substrate such as alumina with two silvered contacts and electrodes in contact with the resistors, all afiixed to the substrate by printing or other suitable techniques. The module is mechanically secured in a depression provided in an insulating gap plate so that one silvered contact is electrically contacted by a spark gap top electrode on one plate. The second silvered contact is contacted by a bottom electrode fixed to the next gap plate of a stacked assembly. With the grading resistors being of equal value and the voltage grading device that spark gap resistors chosen with different values, the stack is balanced except for pre-ionizer sparkover, and at that moment can be unbalanced for any chosen degree of reduced voltage sparkover. Though resistors are shown as the grading impedances, other types of suitable impedances may be used in place thereof or in combination therewith.

For a better understanding of the nature and objects of the invention, reference may be had to the following detailed description taken in conjunction with the accompanying drawings in which:

FIGURE 1 is an elevation view of a spark gap assembly capable of utilizing the novel means of the present invention;

FIG. 2 is a schematic circuit diagram of the spark gap assembly of FIG. 1 wired in accordance with the principles of the present invention;

FIG. 3 is a top plan view of an insulating plate with electrodes and a pre-ionizer-grading resistor module constructed in accordance with the principles of the invention;

FIG. 4 is a partial view of the plate of FIG. 3 taken along lines IV--IV which includes a side elevation view of the resistor module;

FIG. 5 is an enlarged top plan view of the pre-ionizer grading resistor module shown in FIG. 3 and constructed in accordance with the principles of this invention; FIG. 6 is an enlarged side elevation view of module shown in FIG. 5.

Specifically, the invention may be used in an arrester gap assembly that can take the form shown in FIG. 1. Spark. gap assembly 10 can have, for example, a specific voltage rating and can be combined with other identical units and disposed in an arrester housing in accordance with the usual or other techniques to form a complete arrester device having a desired overall voltage rating.

Gap assembly 10 comprises top and bottom end terminal plates 12 and 14 between which there is disposed and retained a stack of gap plates 20 and magnetic drive coil units 16 and 18. In addition, a by-pass capacitor 55 may be disposed between end plate 14 and electrical contact support means 13 suitably connected to a spark gap terminal within one of the intermediate gap plates. Capacitor 55 shorts out a portion of the gap stack with the reception of a fast rise time voltage (say 20 microseconds or less) for the purpose of maintaining an overall low voltage sparkover level. Thus, capacitor 55 and parallel resistors 46 form an RC time constant circuit that makes the gap assembly frequency responsive.

To clarify the manner in which gap assembly 10 is operated in an arrester device, there is shown in FIG. 2 a schematic circuit diagram of the assembly in series circuit relationship with valve or arrester blocks 61 between power line 60, for which overvoltage protection is to be provided, and ground 62. As indicated, assembly 10 includes a plurality of series connected main spark gaps 28 in parallel with resistors 48-49 and 46 having novel and unique operating characteristics to be discussed more fully hereinafter. At each end of the stack is a magnetic drive coil (16 and 18), respectively, protected by bypass gaps 16a and 18a all of which form a part of the subject matter of the above-mentioned copending application.

In FIG. 3 applicants novel and unique pre-ionizer and voltage grading module is shown in place in insulating gap plate 20 that forms a part of the stack depicted in FIGS. 1 and 2. The detailed top plan view of plate 20 (as shown in FIG. 3) shows the plate provided with a peripheral groove 22 and peripheral ridge 21 designed to receive a ridge (not shown) provided on the bottom side of. an adjacent plate to form interfitting means which hold gap plates 20 together. When stacked and fitted together, the top and bottom sides of adjacent plates 20 form respective arc chamber regions within which gap electrodes 30 and 31 and runner electrode 32 are disand spring leaf type of contact 4 posed. In FIG. 3, spark gap electrode 30 and runner electrode 32 are shown mounted on the top side of plate 20 whereas spark gap electrode 31 (shown in dot dash outline) is aflixed to the bottom side of an adjacent plate. When placed together, confronting edge surfaces of elec' trodes 30 and 31 form spark gap 28.

The electrode arrangement depicted in FIG. 3 is given by way of example only, and generally forms the subject matter of the copending application mentioned above. Preferably plate 20 is formed from alumina or glass bonded mica but it can be formed from other suitable materials that are electrically insulating, heat resistant and refractory or nonrefractory.

As best shown in FIG. 4, the novel resistor module 40 of this invention is secured in a tailored depression, between lateral depressions 26, in the top side of gap plate 20 and over which are disposed the ends of the spark gap electrodes 30 and 31 as best shown in FIG. 3. Between gap electrode 30 and the top surfaces of plate 20 and module 40 can be located an electrical spring leaf type of contact means 34 shown in dashed outline in FIG. 3. One end of contact means 34 may be riveted or otherwise secured to and in electrical contact with spark gap electrode 30. The other end is in electrical contact with contact surface 42 provided on the resistor module to be explained more fully hereinafter. Similarly, on the bot tom side of the plate 20 (not shown) and on the bottom side of the next adjacent gap plate, can be disposed a means 35 (shown in dot-dash outline in FIG. 3) fixed on spark gap electrode 31 and electrically contacting surface 43 provided on resistor module 40.

FIGS. 5 and 6 show, in enlarged views, the unique, miniature resistor module 40 of the present invention. The base of module 40 may consist of a substrate formed from any suitable material such as ceramic, glass-bonded mica or other similar materials. On the top face thereof is disposed silvered contact surfaces 42 and 43 and electrodes 4'4 and 45 respectively. Extending between contact surfaces 42 and 43 is a voltage grading resistor 46 and resistor sections 48 and 49. These components may be affixed to the substrate by printing or other suitable techniques. Extensions 44' and 45 of electrodes 44 and 45 can form test pads and contact points that give increased electrode surface contact area in the spark gap region for purposes of electrically checking the circuit module.

Contact surfaces 42 and 43, which may be made of silver or other suitable low electrical resistance metal, form the means for placing voltage grading and preionizing resistors across spark gap 28 formed by electrodes 30 and 31. As previously explained, spark gap electrodes 30 and 31 may have spring contact means 34 and 35, respectively, that press against and rest on silvered surfaces 42 and 43, respectively. Obviously, other means may be provided to form a conductive path between the spark gap electrodes and the silvered contacts 42 and 43, spring contact means 34 and 35 shown for purposes of illustration only.

Grading resistor 46 is in electrical contact with silvered contacts 42 and 43 at its respective ends. Thus, each spark gap 28- has a grading resistor of equal value across it at all times as best shown in the circuit diagram of FIG. 2. This arrangement evenly distributes the line potential across the series of gaps 28, thus distributing the voltage stress evenly over the stacked components of gap assembly 10.

The pre-ionizing gap arrangement with resistors 48 and 49 is disposed on the module substrate in electrical contact with silvered contacts 42 and 43 respectively and with pre-ionizing gap electrodes 44 and 45, respectively, disposed at the lower center portion of module plate 40 and aflixed thereto by printing or other suitable techniques. Pre-ionizing gap electrodes 44 and 45 may be formed of a suitable electrical conducting material such as carbon or silver. Electrodes 44 and 45 form a preionizing gap 47 in conjunction with slot or aperture 50 provided in the substrate of module 40 as shown in FIGS. 5 and 6.

Unlike the equal resistance values of grading resistors 46, resistor combinations 48-49 are chosen with different 1 values so that the moment of sparkover and ionization the stack assembly can be unbalanced to any chosen degree of reduced spark-over voltage level. At the moment a high overvoltage appears on line 60 and gap assembly 10, a second, unbalanced resistance network is placed across main sp'ark gaps 28' through the agency of preionizing gap 47, resistors 48 and 4?, and aperture 50 in the substrate base. Pro-ionizer gap 47 can be set to sparkover, say between 1.1 and 1.5 times the rated voltage. When gap 47 sparkover occurs, main gap 28 is thereby illuminated for consistent sparkover; main gap 28 then fires providing a substantially low impedance path to ground for the surge current produced by the overvoltage. Gaps 2'8 provide a low impedance path to ground in parallel with the two resistance networks composed of resistors 46 and 48, 49 respectively thereby effectively removing them from the circuit for the duration of the sparkover in gaps 28. When the surge current is discharged to ground and ionization ceases, balanced resistors 46 are effectively returned to the circuit. Thus an unbalanced system, with the consequent advantages of lower and stable sparkover voltage levels, returns to a balanced one having the consequent advantage of equal voltage stresses on the stacked components.

Module plate 40, as mentioned previously, is secured in a fitted depression in gap plate 20. The exposed surface of module plate 40 may lie in a plane slightly above the .plane of the surface supporting gap electrode 30 as shown in FIG. 4, or the exposed surface may be flush wit-h the gap electrode supporting surface. The depressions 26 in the gap plate 20 extend along the left and right edges of module plate 40 for purposes of accommodating spring leaf contact means 34 and 35. In this manner good contact is insured between silvered contact surfaces 42 and 43 and the spring leaf contact means.

Thus, a small, voltage grading-pre-ionizing means is provided that neatly fits in the limited area available be tween spark gap electordes contained in gap plates such as shown and described in the copending application mentioned above. Such plates can be easily modified to accommodate applicants novel pre-ionizer-grading module 40. Consequently, the costs of producing such an improved gap and the manufacturing ease of placing and securing the module in the gap greatly enhance the .novelty and uniqueness of the present invention which simultaneously provides a highly efiicient gap assembly because all parts therein are equally stressed, yet unbalanced at the moment of sparkover which provides a lower and consistent sparkover voltage level for the assembly. In addition to these advantages, capacitor 55 can be provided, in parallel with some of the resistors 46, to take over the function of lowering the voltage when very fast time surges make the grading and preionizing resistances less effective. Thus applicants novel and unique combination is also frequency sensitive since capacity 55 and grading resistors 46 form an RC time constant circuit. It should now be readily apparent from the above description and explanation that a novel arrester gap assembly has been disclosed that provides a surety of operation and ease of manufacture heretofore unavailable in the prior art.

While the invention has been shown and described with a certain degree of particularity, changes in detail and arrangement of parts may be made by those skilled in the art. For example, resistor slugs, contacts and electrodes may be attached to module 40 in place of the printed components described. Similarly, other suitable types of grading impedances, such as capacitors, may be :used in place of resistors 46, 48 and 49. Thus the invention is not limited to the specific arrangement shown and described, but is intended to include all modifications which fall within the spirit and scope of the invention.

I claim as my invention:

1. A spark gap device comprising:

a pair of spaced apart electrodes forming a main spark gap therebetween,

means supporting a voltage grading impedance means and a second impedance means on one side thereof, both of said impedance means being electrically connected across the main gap,

a slot provided in the support means,

said second impedance means being separatedinto two parts and disposed on opposite sides of the slot, and

means for preionizing the main gap, said preionizing means including the inner ends of the separated impedance means.

2. A spark gap device comprising:

a pair of's'paced apart electrodes forming a main spark gap therebetween,

means supporting a voltage grading resistor and a second resistor electrically connected across the main p,

a slot provided in the support means, said second resistor being separated into two parts with the inner end portions thereof disposed on opposite sides of the slot,

said inner end portions comprising a preionizing gap for said main spark gap.

3. An arrester gap comprising a stack of insulating plates, each of said plates having a main gap electrode secured on opposite sides thereof, means conductively connecting the gap electrodes associated with each of said plates, each adjacent pair of said plates formed to provide an arc-chamber, the gap electrodes of the confronting plate sides having respective arcing surfaces and confronting portions disposed to provide a sparkover region, a resistor electrically connected to provide a voltage grading path across the gap electrodes, a second resistor disposed adjacent the sparkover region and electrically connected to the main gap electrodes, said second resistor being separated into two parts, and a preionizing gap, said preionizing gap including the inner ends of said separated resistor.

4. A spark gap device having at least one pair of spaced apart electrodes forming a main spark gap, a voltage grading and preionizing means disposed between said electrodes, said means comprising a first resistor disposed on a support member and in electric-a1 contact with the spaced apart electrodes, a second resistor disposed on said support member and divided into two parts, each part having one end in electrical contact with an adjacent electrode of said electrode pair, the other ends of said second resistor being spaced apart and adjacent a slotted recess in the support member between the resistor ends, said ends of the resistor adjacent the slotted recess comprising a small spark gap for preionizing the main gap.

5. The spark gap device of claim 4 in which the resistors are printed on the support member.

-6. A spark gap device having at least one pair of spaced apart electrodes, a voltage grading and preionizing means disposed between the electrodes, said means comprising a balanced voltage grading resistor and an unbalanced voltage grading resistor, electrode means disposed on a support member and in electrical contact with adjacent electrodes of the electrode pair, said preionizing resistor being divided into two substantially equal parts with adjacent ends each having one electrode means disposed on the support member and on each side of an aperture in the support member extending in a direction parallel to the axis of the electrode means and perpendicular to the axis of the resistor parts.

7. The spark gap device of claim 6 in which the resistors and electrode means are printed on the support member.

8. An arrester gap arrangement comprising at least one pair of spaced apart electrodes forming a main spark gap therebetween, the electrodes being generally flat and elongated with the longitudinal axis thereof extending in generally parallel relation, the electrodes having narrow longitudinal extensions on one end thereof with confronting surfaces diverging away from each other to form an enlarged area therebetween, a circuit module disposed in said area and between said confronting surfaces, said module containing a voltage grading resistor electrically connected across said electrode extensions, a second resistor in parallel with the grading resistor and in electrical contact with said electrode extensions, said second resistor separated into two substantially equal sections, and a small spark gap for preionizing the main gap, said small gap formed between the two sections of the separated resistor.

9. The arrester gap arrangement of claim 8 in which the circuit module is printed.

10. An arrester gap arrangement comprising a stack of insulating plates, each of said plates having a gap electrode secured on opposite sides thereof, means conductively connecting the gap electrodes associated with each of said plates, each adjacent pair of said plates formed to provide an arc chamber, the gap electrodes of the confronting plate sides having respective arcing surfaces and 25 confronting portions disposed to provide a sparkover region in a plane substantially parallel to the plate sides, each of said plates having a circuit module secured to one side thereof and disposed between longitudinal extensions of the gap electrodes, said module containing a voltage grading resistor oonnected across said gap electrode extensions and a second resistor connected in parallel with the grading resistor and divided substantially in half, a preionizing circuit adjacent said sparkover region, said preioniz ing circuit formed by the divided resistor, the grading resistors being of equal value to provide equal voltage stress across arrester gap components, the second resistors being of unequal value to provide a lower overall arrester sparkover voltage.

11. The arrangement described in claim 10 in which a capacitor means is connected across at least a portion of the gap electrodes.

References Cited UNITED STATES PATENTS 6/1959 Carpenter et a1. 31559 X 7/1966 Stetson 31536 FOREIGN PATENTS 1,059,657 3/1954 France.

DAVID J. GALVIN, Primary Examiner. 

